title: Protein kinase C inhibition by calmodulin and its fragments.
abstract: Inhibition of protein kinase C (PKC) by calmodulin is investigated and we describe the localization of inhibitory sequences within the calmodulin molecule. We present evidence that calmodulin inhibits PKC through an inhibition of the activation of PKC associated with lipid membranes: Binding of PKC to lipid vesicles is not affected, but activation is abolished. The potent calmodulin antagonist R24571 (calmidazol) did not affect the inhibition of PKC by calmodulin at concentrations up to 10(-5) M. Two tryptic fragments of calmodulin were isolated which inhibited PKC. They were only slightly less potent than intact calmodulin with an IC50 of 6 microM compared to 1 microM of intact calmodulin. They were identified as Ser38-Arg74 and His107-Lys148. Each of the inhibiting fragments contains an intact Ca2(+)-binding domain with complete helix-loop-helix structure ("EF hand"). Other calmodulin peptides showed only weak inhibitory activity. Both fragments did not stimulate cAMP phosphodiesterase even at concentrations 100-fold higher than the calmodulin concentration needed for maximal stimulation. None of the fragments acted as a calmodulin antagonist.
authors.affiliation: Institut für Biochemie, Freie Universität Berlin, F.R.G.
authors.forename: H
authors.initials: H
authors.lastname: Krüger
authors.forename: W
authors.initials: W
authors.lastname: Schröder
authors.forename: K
authors.initials: K
authors.lastname: Buchner
authors.forename: F
authors.initials: F
authors.lastname: Hucho
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D006657:Histones / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D008563:Membrane Lipids / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology*; D010766:Phosphorylation; D011487:Protein Conformation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D014357:Trypsin
chemical_list: D002147:Calmodulin; D006657:Histones; D007093:Imidazoles; D008563:Membrane Lipids; D010446:Peptide Fragments; C031938:calmidazolium; D011493:Protein Kinase C; D014357:Trypsin; D002118:Calcium